Method of bleaching cellulose derivatives



Patented Dec. 15, 1953 JOQ UNITED STATES PATENT OFFICE METHOD OF BEEACHING CELL ULOSE DERIVATIVES Roy H. J enkins, In, Hopewell, Va, assig'lml'- to Hercules Powder Company, Wilmington, mm, a corporationofDelaware no Drawing; Application May 17,. 1951,v Serial; No. 226,930

15' Claims.

I This invention relates to the treatment of cellulose derivatives. Ina specific aspect this invention relates to a process for the treatment of cellulose ethers. In one of its specific aspects this invention relates to aprocess for the bleaching and removal of color bodies from a cellulose ether by a novel bleaching operation In the production of cellulose ethers, for example, carboxymethylcellulose, hydroxyethyl cellulose, and the like, it has been noted. that color bodies are formed. during such: steps as the viscosity regulation by the use of viscosity reducing agents, such as hydrogen peroxide and. manga nese sulfate. The color bodies: are not entirely removedby subse uent Washing operations, and the color is noticeable in aqueous solutions of the cellulose ether. Cellulose-others prepared from cotton linters are not subject to this color degradation to the same extentas cellulose ethers prepared from wood pulp.- Consequently, this invention. is particularly useful and adaptable to those cellulose others prepared from wood pulp, but the invention is also applicable to the cellulose ethers prepared. from cotton Ii-nters. In view o-tthe fact that the presence of color bodies incellulose ethers is frequently undesirable. the importance of anefficient bleaching operation for removing such color bodies from. the cellulose ether is quite evident. c

It is an object at this invention to provide a novel process for the treatment of cellulose derivatives.

It is another object of this. invention to provide a novel process. for the treatment of cellulose others.

It is another object of this invention to provide a} novel. process for the bleaching and removal of color bodies from a cellulose ether.

It is a further object of this invention toprovide a riovel. process for the bleachingand removal of color bodies from acellulose ether, such as carboxymethylcellulose. carboxymethyl hydroxy-- ethyl cellulose, and hydroxyethyl cellulose in a slurry withanonsolvent for-saidether.

Further and addition objects of this invention will be apparent from. the detailed. disclosure and description of the invention. 7

In. accordance with this invention ithas been found that cellulose ethers can be elhciently and efi'ectively bleached and color bodies removed from. the cellulose other by contacting, a slurry of the cellulose ether in an inert nonsolvent for the other with a chlorite bleaching agent. When the slurrying medium is acidic, the chlorite is 3 910118 t e ea h ng gent When aneua tral or alkaline slurrying medium is employed, the chlori'te is activated with a hypochlorite in order to effect the desired bleaching. I

The following specific examples are illustrative of this invention.

Example 1.

One hundred ten grams or carboxymethyl cellm lose wet with isopropanol grams c'arboxymethylcellulose on a dry basis) was. slurried' in 1325 cc. methanol at room temperature (4.1% slurry concentration) and 025 gram of a 25% aqueous sodium chlorite solution and 0.5 gram sodium hypochlorfte solution (6% available chlorine) were added. The pH was adjusted to 6.5 to 7.5 with glacial acetic acid, and the slurry agitated for 0.5 hour. The carboxymethylcellulose was then filtered; batch washed with two 1500 cc. portions of 85 methanol, and dried in aforced air drier. ori inal carboxymethylcellulose had a 2% solution color of 3.5; the; bleached carboxymethylcel-Iulcse had a soIution color of 1.0.

Exam le 2 One hundred ten grams of carboxyinetnylcell'ulose wet with. isopropanor (so grains carboxymethyleellolose on a dry basis) was slurried r325 cc.- 85% methanol at. room tem erature (4.3% slurry concex'itration), and 0.25 gram or a 25% aqueous sodium chlorite solution. and 1.0 gram sodium hypochloritc solution 66% available chlorine) were added. The pH was ad u'sted to 6.5 to 7.5 with glacial acetic acid, and the slurry agitated for 0.25 hour; The carboxymethylcellulose was then. filtcred batclr washed with two 1500 portions of 85% methanol, and dried aforced air drier.- The original. carbcxymethylcellulose had a 2'75v solution color of. 3.5 the bleached carboxymethyicellulose had a solution color of Ml.

Example 3 p Two hundred twenty grams or carboxymethylf cellulose wet with isopropanol (r00 grams carboxymethwlcell-u-lose on. a dry basis) was slurried in 780 cc. methanol at room temperature (10.0 slurry concentration) and 0.5 gram of a 25% aqueous sodium chlorite solution and 1.0 gram. sodium hypochlorite solution (6% available chlorine) were added. The pI-I'was adjusted to 6.5 to 7.5 glacial acetio one. and the slurry agitated for 0.5 hour. The carboxymethylcelhi lose. was then izllztemdr batchwashed with two 1500 portions or 85% methanol. and dried a fiorced air drier; The carboxvmethyl cellulose had a 2% solution color of 3.5; the bleached carboxymethylcellulose had a solution color of 1.5.

Example 4 One thousand seven hundred fifty grams of a carboxymethylcelluloseslurry in 87% isopropanol (6.7% carboxymethylcellulose) was neutralized to a pH of 7.0 with phosphoric acid, and heated to 60 0. Then 2.2 grams of a 25% aqueous sodium chlorite solution and 4.2'grams of sodium hypochlorite solution (6% available chlorine) were added. The slurry was agitated 0.5 hour at 60 C. The carboxymethylcellulose was then filtered, washed once with 1500 cc. 100% methanol, and dried in a forced air drier, The original carboxymethylcellulose had a 2% solution color of 4.5; the bleached carboxymethylcellulose had a solution color of 1.5.

Example 5 tion color determinations, which method is described in ASTM Book of Standards, 1939, Designation D365-39, page 804. In this method, known as the platinum-cobalt color standard, 1.246 grams of potassium platinic chloride and 1000 gram of cobalt chloride are dissolved in 2:8; for a No. 3 color standard the volumetric and the carboxymethylcellulose filtered, batch washed with two 1500 cc. portions of 85% methanol, and dried in a forced air drier. The original carboxymethylcellulose had a 2% solution color of 3.5; the bleached carboxymethylcellulose had a 2% solution color of 1.0.

Example 6 Thirty grams dry carboxymethyl hydroxyethyl cellulose was slurried in 370 grams 87% isopropanol (7.5% slurry concentration), and 0.6 gram of a 25% aqueous sodium chlorite solution and 4.3 grams sodium hypochlorite solution (6% available chlorine) were added. The pH of the slurry was 7.7, so no additional pH adjustment was necessary. The slurry was agitated for 0.5 hour at room temperature. The carboxymethyl hydroxyethyl cellulose was then filtered, washed twice with two 1500 cc; port ons of 100% methanol, and dried in "a forced air drier. The original carboxymethyl hydroxyethyl cellulose had a 2% solution color of 6.0; the bleached carboxymethyl hydroxyethyl cellulose had a solution color of 1.0.

Example 7 One hundred fifty grams of dry hydroxyethyl cellulose was slurried in 1850 cc. of 87% isopropanol at room temperature (9% slurry con centration), and the 'p'H adjusted to 6.8 to 7.0 with acetic acid. Three grams of a 25% aqueous sodium chlorite solution and 6.0 grams sodium hypochlorite solution- (6%;-available chlorine) were added. The pH was raised to 8.4 by addition of the sodium hypochlorite, so pH was readjusted to 7.0 with acetic acid, and the slurry agitated for 0.5 hour. Thehydroxyethyl cellulose was then filtered, batch washed with two 1500 (:0. portions of 100% methanol and air dried in a forced airdrier. The original hydroxyethyl cellulose had a solution color of 4.0 (2% hydroxyethyl cellulose in 5% sodium hydroxide); the bleached hydroxyethyl cellulose had a solution color of 2.0. 1 l r In the above examplesthe solution colors were determined by a methodsimilarto that em:- ployed for nitrocellulose and ethyl cellulose soluproportions are 3:7. By comparison with these color standards the color determinations in the above examples were made.

The cellulose ethers within the scope of this invention are organic solvent-insoluble, and the ethers can be either alkalisoluble or water-soluble or soluble in both alkali and water. The degree of substitution, i. e., the number of substituent radicals per anhydroglucose unit, of the cellulose ethers will be such that the cellulose ether to be bleached has these properties. Actually, carboxymethylcellulose, carboxymethyl hydroxyethyl cellulose and hydroxyethyl cellulose are either alkali-soluble or water-soluble in all degrees of substitution. Among the cellulose ethers that can be bleached in accordance with this process are the alkyl cellulose ethers, for example,

ethyl cellulose, propyl cellulose and butyl cellulose; hydroxyalkyl cellulose ethers, for example, hydroxyethyl cellulose; carboxyalkyl cellulose ethers, for example, carboxymethylcellulose, carboxyethy cellulose, carboxybutyl cellulose, and the like; carboxyalkyl hydroxyalkyl cellulose ethers, for example, carboxymethyl hydroxyethyl cellulose; and sulfoalkyl cellulose ethers, for example, sulfoethyl cellulose. In addition to the above cellulose ethers, ether-ester derivatives of cellulose can also be bleached in accordance with this process, but in these ether-ester derivatives the ether grouping is the dominant substituent. For example, it is within the scope of the invention to employ acetylated hydroxyethyl cellulose wherein the hydroxy ether grouping is the dominant substituent, and the acetyl radical is present only in a minor amount.

The cellulose ethers within the scope of this invention can be prepared by any of the known methods of preparation. Since the invention is particularly applicable in its preferred form to such cellulose ethers as carboxymethylcellulose and carboxymethyl hydroxyethyl cellulose, specific methodsfor preparing such cellulose ethers will be described. One of the preferred methods of preparing carboxymethyl hydroxyethyl cellulose is the slurry process wherein cellulose is reacted with an hydroxyalkylating agent such as ethylene oxide in the presence of a slurrying medium such as isopropanol and a caustic alkali, for example, sodium hydroxide. To the resulting reaction mixture is added a carboxyalkylating agent such as monochloracetic acid, and the resulting mixture. is agitated for a period of time sufiicient to effect the desired reaction. It is within the scope of the invention to bleach the carboxymethyl hydroxyethyl cellulose by addition of the bleaching agent to the resulting re action mixture or, if desired, the cellulose ether can be recovered and bleached as described more .iul yher inafter. .Cas o ya kyl ce lulose et eis, for example, carboxymethylcellulcse, g: he rs,- ated by a sim lar slurry proc ss wh ch .invo y rea t ng cellulose n t e p ence o e ca st c alkali with a carboxyalkylating agent such as mon ch o ac ti ac d in a slur :m cl um o p ng a l w boiling al phat c coh si eferably isopropyl alcohol or tertiary butyl .alcohol. Ifhe r su t g mixture is ag tat d ra p iod of t me .sutfici nt o fiect the desired rea on. and at the n o that time the resu t ng cel ul e/ether can b b e h the rea t m xture lay prac cin th invent on. Alt rn t ely. the ce lul s eth can be recov red f om the eaction mixt re nd hen b eached-as d sc ib d hereinait r- It wil h n e stood by th se ski le the art that the above m h ds of p epar ng cellll ose .et e s a e mer ly illu r tive and th t eel lulose th r prepa ed y th se meth ds o a y other-me hod ca be bleache by this process.

The slurrying media that are employed in practici g th i v t on ar inert water misc ble organic liquids which are nonsolvents for the cellulos e he to be lea h d. TXD BJ xa n of the slurrying media that can be employed are L the lower alphatic alcohols, for example, methan l, ethyl alc h isopr hyl a ohol, tertiary butyl alcohol, and the lik Wh n the zil v nt on is employed to ach cellul s etheits prepared by the slurry process, it is apreierred to employ either .isopropyl alcohol or tertiary butyl a cohol inc th se o ls a e pieie ned as th lur yine med um for t ormat on of th c llulose ether. Among the other organic liquids that be used to slurry the cellulose ether are d oxane. t trahydrcfu n. th di hyl eth r of ethylene glycol, and the like.

Iihe b eaching ent t at i mploy d in practicing this invention is a chloiiite, preferably a metal .chlorite, but .nonmetallic chlorites, such as ammonium .ohlorite, can also be used. preferred metal chlorites are the alkali metal and alkaline earth metal .chlorites, for example, odium ch i e. potassium chlol'ite. ca c um chlc ite, magnes um ch or e. and the like. sod um h rc is t p e ed bl chin agent th t is us d in prac n th s i v nti Th chlcn e b e ch n a ent is u ually added to h slu ryi medium conta nin the cellulose ethe in th te m o n aque us solut on ontainin from 1 to 25% by weight of :the chlprite. The amount o t hloi' te qu red to ef ect the desired bleaching is variable. However, joy .all practica r o e i has been found that the sl sired bleaching can be eiiected by emploflng from 0.;125 to 3% by Weight of the chlorite based on the cellulose ether to be bleached. It has o been ice-ml that the chlorite alone is efiective for bleaching cellulose vethers only when the slurrying medium is substantially acidic, i. e., when the slurrying medium has a pH lower than 6. When the slurrying medium is neutral, i. e., when its .pH is within the range of '6 to 8, or when the slurrying medium is alkaline and has a 13H higher than 8, the chlori-te alone does not effect the desired bleaching of the cellulose ether, and actually at a pH higher than 8 the bleaching action oi the chlorite is rather slight. However, in a neutral or alkaline medium, the cellulose ether can be bleached with a ch'lorite bleaching agent by activating the chlorite with a hypocl' loi ite. Vari u hypoch orites can be e-pla to effect the desired activation of the chlorite bleaching agent. The preferred hydrochlorites are the metal hypochlorites such as the alkali metal and alkaline metal hypoehlorites. and th chest nheierrediactiyattins agent-is sodium hyhochlcrit filihe amount .oi hyp chlorite that is r el-tire is sociable, and g nerally from 11.5 to :by weight theses em ce lulose ether) or .a hype hlorite solution about 6 available chlorine seifcct e, When using a chlorite activated with ayhypochhariteztolblcacha cellulose o her, i is preform d to effect the desired hleaching "with a slurrying medium having a pH Within the range of 6 to .8- .Sin e the hyp chlonite, icr exam-ri e. dium hypcchl r e, is on st le a sliirsying m di m s ch as iscpr p l alcohol a d methyl alcohol, it is necessary to adjust the PH i th shi ryine med um with an ac d within n t more than l5 minutes after the hyhech ori introdu ed to the slhrryine m dium. :15 procedure n t followed. most of the bleaching action will be l st. If desired, the pH o the :slu lt ihe medium can be i-adiusteo be ore the chlcrite and/or the hypochlorite is dded, but in most "ins ances a li ht adjustment of th his w ll be sem -reel fter introduction of the hyp echl rite because of its alk linits- :I-lypochlorites, nch as sodium hypoehlorit are n t eilecti e J01 bleaching thes cellulose others. fact was determined when the bleaching of carboxym thv cel ul s was ttempted with sod um :h i h orite. and t was ioimd that the color improvement. if an wa negligible. In one run using 25% sodium hynoehlor-ite (based on the carboxymethylcellulose at a nil o 10.4 the col r of the resultin carboxymethvlcellol se 4.0, and the color of the ori inal .oanboxymethylcellulose was 3.5.. In a simi ar at a PH of 7.0 the color of th carboxrymethyleellulose was unchanged from its original color of 3.5.

.As indicated ab ve. this invent on is ideally uite for the bl aching oI cellulose ether prepared accordance with the slurry process which has already h en discus ed. If de ired, t bleaching operation can he eflected by addition of the bleachin a ent to the reaction mixture of sins. he medium and cellulose ether. On the ther hand. the cellulos eth r can b p rated from th ea tion mixture and, at a subs q me, h ether :is slurried in on of the or anic slum/ ns media discussed above, Th con entration of the slurhy :i gener ll W in he ran of 3 to :15 we ht per nt. Higher concentrations are not desired since at snch high concentrations tfic ent agitati n of he. slurry is difficult to obtain.- Also lower concentrations cn be used, but since they are not necessagy, they are not normal- 11v em neyed order to avoid handli g 1mnecessarily large quantity of slurrying medium. Aiter formatio of. the slurry of organic liqu and cellulose ether, the bleaching operation s effected by addition of either the chlorite or the chlori =hirncchlorite mixture.

It is one the advantages of this invention hat the bleachin of the cellulose other can be effected over a. wide temperature range. The bleaching process can be carried out at room emperature. and the preferred temperature range varies from 20 to 160- C. However, it will beunderst osl that hi her ansl'low r t mperatures can, "be use if. desih d. but higher temperatures are i esi by the boiling po nt f th slurrying medium. order eiieet the desired bleaching the slurry containing the cellulose ether and bleachin gent is agitated w th a mechanic l mixer or by other suitable means for a period of time sufilcient to carry out the desired bleaching.

ing operation is within the range of to 120 minutes. At the end of that period of time the bleached cellulose ether is separated from the slurry by suitable means such as filtration, centrifuging, decantation, and the like, and after drying the bleached cellulose ether is then ready for other processing or shipment.

In order that the pH of the slurrying medium can be maintained within the desired range, it is usually necessary to adjust the pH by addition of an acid to the slurry. Various organic and inorganic acids can be used to effect this pH adjustment. For example, acetic acid, has been found to be quite efiective, and strong mineral acids, such as hydrochloric acid, and the like, are suitable for pH adjustment. Phosphoric acid can also be used for pH adjustment and, in some instances, it is preferred to employ phosphoric acid. It is well known that metal chlorites, such as sodium chlorite, are undesirably corrosive when in contact with metallic surfaces. However, when phosphoric acid is employed to adjust the pH, the phosphoric acid also inhibits the corrosive action of the sodium chlorite. Therefore, in those instances where an acid slurrying medium is employed and when the vessel in which the bleaching is effected is corrodible when in contact with a metal chlorite, it is preferred to adjust the pH of the slurrying medium with phosphoric acid.

This invention possesses numerous advantages over other bleaching operations. For example, the sodium chlorite is particularly adapted to the bleaching of water-soluble cellulose ethers made by the slurry process because the sodium chlorite is stable in the organic solvent slurrying medium. Also, the sodium chlorite does not tend to degrade the cellulose ether and thus cause an undesirable viscosity reduction of the ether. Further, the invention permits the bleaching of the cellulose ether in an acid, neutral or alkaline medium, and the bleaching can be carried out over a relatively wide temperature range, thus making unnecessary the use of any jacketed bleaching vessels. Also, regular types of stainless steel vessels can be employed to carry out the bleaching process since in a neutral or alkaline medium, the chlorite bleaching agent is not corrosive and in an acid medium its corrosive activity can be inhibited by proper selection of the acid for pH adjustment. 1

Numerous modifications and additional advantages of the process will be readily apparent to those skilled in the art.

What I claim and desire to protect by Letters Patent is:

1. The method of bleaching and removing color bodies from an organic solvent-insoluble cellulose ether which comprises contacting a slurry of said cellulose ether in an inert watermiscible nonsolvent for said cellulose ether with an inorganic chlorite, said chlorite being activated with an inorganic hypochlorite when the pH of said slurry is not lower than 6.

2. The method of bleaching and removing color bodies from an organic solvent-insoluble, water-soluble cellulose ether which comprises contacting a slurry of said cellulose ether in a water-miscible, lower aliphatic alcohol with an alkali metal chlorite activated with an alkali metal hypochlorite at a pH not lower than 6.

3. The method according to claim'2 wherein the cellulose ether is a water-soluble carboxymethylcellulose.

4. The method according to claim 2 wherein the cellulose ether is a water-soluble carboxymethyl hydroxyethyl cellulose.

5. The method according to claim 2 wherein the cellulose ether is hydroxyethyl cellulose.

6. The method of bleaching and removing color bodies from an organic solvent-insoluble, water-soluble cellulose ether which comprises forming a slurry containing from 3 to 15% by weight of said cellulose ether in a water-miscible, lower aliphatic alcohol, adding to the slurry thus formed from 0.125 to 3% by weight of sodium chlorite based on the celluluose ether and from 0.5 to 4% by weight of sodium hypochlorite based on the celluluose ether, adjusting the pH of the resulting mixture to a pH within the range of 6 to 8, and agitating the mixture thus forfned for a period of 5 to minutes at a temperature within the range of 20 to 60 C.

7. The method according to claim 6 wherein the alcohol is isopropanol.

8. The method according to claim 6 wherein the alcohol is methanol.

9. The method of bleaching and removing color bodies from an organic solvent-insoluble, water-soluble cellulose ether which comprises contacting a slurry of said cellulose ether in a water-miscible, lower aliphatic alcohol with an alkali metal chlorite at a pH lower than 6.

10. The method according to claim 9 wherein the cellulose ether is a water-soluble carboxymethylcellulose.

11. The method according to claim 9 wherein the cellulose ether is a water-soluble carboxymethyl hydroxyethyl cellulose.

12. The method according to claim 10 wherein the cellulose ether is hydroxyethyl cellulose.

13. The method of bleaching and removing color bodies from an organic solvent-insoluble, water-soluble cellulose ether which comprises forming a slurry containing from 3.to 15% by weight of said cellulose ether in a water-miscible, lower aliphatic alcohol, adding to the slurry thus formed from 0.125 to 3% by weight of sodium chlorite based on the cellulose ether, adjusting the pH of the resulting mixture to a pH lower than 6, and agitating the mixture thus formed for a period of 5 to 120 minutes at a temperature within the range of 20 to 60 C.

14. The method according to claim 13 wherein the alcohol is isopropanol.

15. The method according to claim 13 wherein the alcohol is methanol.

ROY H. JENKINS, JR.

References Cited in the file'of this patent UNITED STATES PATENTS Number Name Date 1,948,517 Dreyfus Feb. 27, 1934 2,109,509 Schneider Mar. 1, 1938 2,138,757 Collings et al. Nov. 29, 1938 2,238,192 McHard Apr. 22, 1941 2,358,866 MacMahon Sept. 26, 1944 FOREIGN PATENTS Number Country Date 561,834 Great Britain June 7, 1944 OTHER REFERENCES Taylor et al.: Technical Assn Papers, 1940, pages 251-254. 

1. THE METHOD OF BLEACHING AND REMOVING COLOR BODIES FROM AN ORGANIC SOLVENT-INSOLUBLE CELLULOSE ESTER WHICH COMPRISES CONTACTING SLURRY OF SAID CELLULOSE ETHER IN AN INERT WATER MISCIBLE NONSOLVENT FOR SAID CELLULOSE ETHER WITH AN INORGANIC CHLORITE, SAID CHLORITE BEING ACTIVATED WITH AN INORGANIC HYPOCHLORITE WHEN THE PH OF SAID SLURRY IS NOT LOWER THAN
 6. 